A goldfish bowl full of water, we know, has a distorting effect on its inhabitants. The convex glass means that at one moment the twinkly fish circling the bowl seem minuscule, while at the next an eye looms up at the apparent size of a marble.

Perhaps it would have been a good idea for Cherie Booth to have pondered this optical illusion when she put together a study of the lives of Prime Ministers' wives with her friend, documentary maker and social historian Cate Haste.

For although the goings on inside Number 10 are periodically fascinating, say, in the middle of a scandal or a political crisis, they are, at other times, bound to look trifling and irrelevant.

For instance, the public was only briefly curious about what dinner times were like for Norma and John Major once they belatedly understood that, for a while at least, Currie was not a family favourite. For the rest of the time, we were content to imagine them scooping up their peas on forks and dressed in grey, like their caricatures on Spitting Image.

In some respects, then, it was lucky for Booth and Haste's joint project that Melvyn Bragg made his veiled reference to serious domestic stress in the Blair household when he did.

When the television presenter (and long-time partner of Haste) suggested in a recent television interview that the Prime Minister had just gone through a troubled patch in his private life, suddenly the goldfish bowl's magnifying effect was in operation with a vengeance and family matters inside Downing Street took on a greater significance.

How on earth, we wondered, do the Blairs cope with constant observation and the pressure of work? The book's potential readership could not have been more agog.

But the answer to this question is not found here. Instead, the book offers a mildly diverting survey of the views of the women (and the spouses are all wives, apart from Denis Thatcher) who have supported our country's leaders since 1955. The narrative pulls up abruptly at the instant the big black door closes behind Cherie and Tony in 1997.

As a result, all readers get is an informed peek into the backrooms and kitchens of history. It is a jolly format, but unfortunately the canvas is rather too large and the people depicted too disparate for a binding theme to emerge. There is, it's true, an overarching feminist argument visible every now and then, but it is rather a hazy one and there are perhaps not enough examples of the slights and inconveniences suffered by wives over the years to strengthen this line.

We do learn that when the news finally broke of Major's affair with Edwina Currie, it efficiently blighted an important Mencap charity event that Norma had been arranging for a year. She put it down, with saintly stoicism, to 'Sod's law', but the underlying point is that she, like all PM's wives, cannot really be heard to complain about her lot too vociferously because she would quite possibly never have been in a position to organise such a large-scale public event, or to have her own books published, if she had not married a future Prime Minister.

Entertaining though the social insights thrown up by the contrasting backgrounds of 'first families' since the 1950s are, because of the wide scope of this study it is short on political context. This means the anecdotes that stand out are the naughty ones, the ones that offer a glimpse of family intimacies, or the lack of them.

Over the decades, officials are repeatedly described barging into the Prime Minister's private apartment and even into his bedroom. So intrusive are the PM's aides that Clarissa Eden, wife of Sir Anthony, once declared she did not remember having one meal alone with her husband while he was in office.

Cherie's personal contributions contain just the occasional hint of her own view. She does refer feelingly in passing to a sense that family life in Downing Street is successively 'sacrificed to the machine' and elsewhere to Tony having to take calls on a satellite phone even when he is climbing a mountain.

She also highlights the fact she is the only mother to have raised young children at Number 10 since the tenure of the Asquiths, but there is no mention of the much-rumoured accommodation 'issue' with the Browns (who actually live in the smaller flat above Number 10).

The only morsel we are offered is that Norma got the kitchen updated and that the larger flat in Number 11 (where the Blairs live) did not have a shower when Cherie arrived.

Ultimately, of course, these are rather naive criticisms since this book is clearly a political work. It's not political in the parliamentary sense, although there is a jibe at Thatcher for not putting more women in the cabinet, but the fact is that Cherie still has to be guarded. Whenever this accomplished and opinionated woman has thrown caution aside and spoken out, it rebounds on her horribly.

This will not always be the case. So what we have here is a coffee-table book that also serves as a marker reading 'watch this space'.